1. Field of the Invention
The present invention relates to a disk control apparatus employed for a disk system apparatus that enables data to be stored in plural magnetic disk units.
2. Description of Related Art
Many efforts have been made to bring input/output performance of a disk subsystem (referred to as subsystem, hereinafter) which uses magnetic disks as recording media, close to that of a computer equipped with main memory, which uses a semiconductor storage unit as recording media, because the performance of the former is as low as about 1/1000 to 1/10000 of that of the latter.
Employment of a disk control apparatus that enables data to be stored in plural magnetic disk units is one of the methods for improving the input/output performance of the subsystem.
For example, the conventional well-known disk control apparatus shown in FIG. 6 includes one or more disk control clusters (referred to as the cluster, hereinafter) 101 in addition to plural channel interface units 10 used to transfer data between a host computer 60 and the cluster 101, plural disk interface units 20 used to transfer data between a magnetic disk unit 70 and the cluster 101, a cache memory unit 30 used to store data to be read/written from/in the magnetic disk unit 70, and a resource management unit 90 used to store information related to the cluster 101 (for example, information related to the controlling of the data transfer between each of the channel interface units 10/disk interface units 20 and the cache memory unit 30, and management information of the data to be stored in the magnetic disk unit 70).
The disk capacity and the number of host channels connectable to one cluster 101 are limited. When data must be stored over the limited disk capacity and/or when host computers 60 in a number larger than that of host channels that can be connected to one cluster have to be connected, therefore, the disk control apparatus is provided with plural clusters 101.
A data path network 400 is used for the connection between each of the plurality of channel interface units 10/disk interface units 20 and the cache memory unit 30 over the plurality of clusters 101.
Similarly, a resource management network 500 is used for the connection between each of the plurality of channel interface units 10/disk interface units 20 and the resource management unit 90 over the plurality of clusters 101.
Consequently, the resource management unit 90 and the cache memory unit 30 can be accessed from every channel interface unit 10 and every disk interface unit 20.
Each of the channel interface units 10 includes an interface with a host computer 60 and a microprocessor (not shown) for controlling the input/output to/from the host computer 60.
Each of the disk interface units 20 includes an interface with a magnetic disk unit 70 and a microprocessor (not shown) for controlling the input/output to/from the magnetic disk unit 70.
The disk interface unit 20 is also used to execute the RAID functions.
The data path network 400 is configured so as to include one or more switches 80.
When data is transferred from a channel interface unit 10/disk interface unit 20 to the cache memory unit 30 through the data path network 400, packets are used for the data transfer. Each packet includes a destination address added to the initial position of the data written therein.
The transfer of those packets to the target cache memory unit 30 through the data path network 400 is controlled by the microprocessor provided in each channel interface unit 10 or disk interface unit 20.
Each switch 80, as shown in FIG. 7, includes plural path interfaces 41 connected to the data path network 400, plural packet buffers 43 and plural address latches 44, as well as a selector 48.
In each path interface 41, a header analyzer 42 is included. The header analyzer 42 is used to take out address information from each packet, thereby the analyzed and extracted packet address is fetched into the corresponding address latch 44.
On the other hand, received packets are stored in a packet buffer 43 through the corresponding path interface 41.
Each address latch 44 generates a selector control signal 47 according to the destination address of each packet and the selector 48 selects a path to the destination address of each packet stored in the packet buffer 43.
In this way, the path change for each packet in the conventional switch 80 is decided fixedly by the packet address.
This is why a path of packets through the data network 400 must be preset under the control of the microprocessor built in the subject channel interface unit 10/disk interface unit 20.
Especially, when a packet is to pass plural switches 80 provided in the data path network 400, the path change information for those switches 80 is added to the packet in prior to the transfer.
The latest business environment, which is rapidly changing day by day, demands a high scalability disk control apparatus that allows a user to expand his/her business facilities step by step while suppressing his/her initial investment cost.
Such disk control apparatus needs to have high scalability that can cope with various scales of company's facilities, ranging from small to very large scale, to meet the users' needs. This demands that the apparatus needs to have flexibility to cope with the number of channels for connections to host computers, as well as with data capacity of each of its magnetic disk units.
The conventional techniques shown in FIGS. 6 through 8 have been difficult to flexibly change the configuration of the channel interface unit/disk interface unit for the connections to the host computers in correspondence with the users' needs, since a microprogram presets the path on the way in the data bus network 400 between each of the channel interface units 10/disk interface units 20 and the cache memory unit 30.
In addition, the packet traffic in the data path network 400 has a partiality. Any of the conventional techniques described above, which fixes the path of packets cannot realize path optimization while the path for packet transfer can be optimized to increase the total number of packets to be transferred in the data path network 400.
This is why the performance of the disk control apparatus has been degraded significantly due to the band limitation of the data path network 400 while the number of the channel interface units 10/disk interface units 20 increases.
Furthermore, when the disk control apparatus is configured by plural clusters 101, the microprocessor in each channel interface unit 10 or disk interface unit 20 is required to control every switch 80 in the path for path changes. Along with an increase in the number of the clusters 101, the connections to those clusters 101 come to be complicated, the processing load of the microprocessors increases, thereby the data transfer to/from the host computer 60 and the magnetic disk unit 70 is often disturbed. This is why the performance of the disk control apparatus has been degraded.
Under such circumstances, it is an object of the present invention to provide a disk control apparatus configured so as to realize scalability and enabled to change the configuration to a smaller/larger one with the same enhanced architecture of a high reliability, as well as to solve the problems of the conventional techniques.
More concretely, it is an object of the present invention to provide a disk control apparatus to be expanded flexibly in correspondence with users' requirements and enabled to adjust the connection state therein as needed, and furthermore to provide a disk control apparatus whose performance is prevented from degradation more effectively even in a configuration having a very large cluster scale.